Coating manufacturers have achieved significant progress in developing novel components for polyurethanes to improve coating properties, although a need remains for novel catalyst systems. Typical catalysts for making polyurethanes are dibutyltindilaurate and tertiary amines.
Organometallics of the group 14 elements, particularly dibutyltin derivatives, are known to catalyze transesterification, transcarbamoylation and urethane formation. While there has been significant progress to develop novel components for polyurethanes to improve coating properties, a need remains for novel catalyst systems for use in making the polyurethanes. Typical catalysts are dibutyltindilaurate and tertiary amines. Dialkyl and trialkyltin derivatives, classes of the compounds to which dibutyltindilaurate belongs to, have some toxicity to humans, further driving a need for new, less toxic catalysts. New processes for forming polyurethanes are also desired.
Jousseaume, B. et al., (“Air Activated Organotin Catalysts for Silicone Curing and Polyurethane Preparation” (1994) Organometallics 13:1034), and Bernard, J. M. et al. (U.S. Pat. No. 6,187,711) describe the use of distannanes as latent catalysts, e.g. Bu2(AcO)SnSn(OAc)Bu2. Upon exposure to air, such species oxidize to give distannoxanes, e.g. Bu2(AcO)SnOSn(OAc)Bu2, which are known to be highly active for urethane formation. However, the carboxylate-substituted distannanes are themselves catalysts for the reaction, and have been reported to be “relatively stable in air”, which suggests that oxidation to form an active catalyst is slow. See U.S. Pat. No. 3,083,217 to Sawyer et al. UV light appears to be necessary in order to induce oxidation at an appreciable rate in these distannanes. Thus, there exists a need for a catalyst precursor that, in the absence of air, is a very poor catalyst and yet, upon exposure to air, rapidly forms a highly active catalyst that allows for rapid cure.
Co-owned and co-pending U.S. patent application Ser. Nos. 11/154,387 and 11/154,224 describe air activated organotin catalysts without protecting groups. While the catalysts described in these applications are latent, i.e. active only in the presence of air, they lose their latency upon prolonged exposure to isocyanate. As a result, they cannot be stored in isocyanate. Moreover, because they are air-sensitive, they must be kept from air until spray application.
Co-owned and co-pending U.S. Pat. applications (CL-3032 and CL-3268) describe how the catalysts of U.S. patent application Ser. Nos. 11/154,387 and 11/154,224 can be protected using labile protecting groups, which render them stable in air and stable in isocyanate, at least for several days. Upon contacting a isocyanate solution of the protected catalyst with an alcohol, optionally in the presence of acid, the catalyst is deprotected and can be activated by air during the spray application process.
Co-pending and co-owned U.S. Pat. applications (CL-3191, CL-3280) disclose divalent tin and germanium compounds and their use as catalysts. (CL-3191) discloses divalent derivatives of tin stabilized by bulky phenoxy groups. (CL-3280) discloses divalent tin and germanium compounds stabilized through bulky chelating P^O ligands.
The present invention provides processes using, as catalysts, quadrivalent tin and germanium compounds containing more than one triorganylsilyl groups connected to tin or germanium.
The catalytic use of the materials described herein, for the production of polyurethanes, has not been heretofore disclosed.